1. Field of the Invention
The present invention relates to a thin film magnetic memory device, and more particularly, to a random access memory including memory cells using a magnetic tunneling junction (MTJ).
2. Description of the Background Art
Recently, attention has been paid to an MRAM (Magnetic Random Access Memory) device as a new generation nonvolatile memory device. The MRAM device is a nonvolatile memory device which stores data in a nonvolatile manner using a plurality of thin film magnetic elements formed on a semiconductor integrated circuit and which enables each thin film magnetic element to be randomly accessed. It is made public that the performance of the MRAM device is surprisingly developed particularly by using thin film magnetic elements utilizing a magnetic tunneling junction (MTJ) as memory cells in “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, 2000 IEEE ISSCC Digest of Technical Papers, TA7.2.
Generally, in the case of performing the storage of data in each memory cell used as a memory element in the nonvolatile memory device or MRAM device, data is written by applying a predetermined voltage and supplying a current to the memory cell. In this MRAM device, a predetermined data write current is supplied to the memory cell and a desired magnetic field based on the data write current is applied to the thin film magnetic element, thereby performing data write by which the magnetic direction of the thin film magnetic element changes.
However, various wirings used for various purposes including a wiring for supplying a data write current are arranged in the MRAM device, and a magnetic field is generated when a current is carried to each of these various wirings. In this case, magnetic field noise is often applied to unselected memory cells other than a selected memory cell.
Such magnetic field noise may possibly change the magnetic direction of the thin film magnetic elements of the unselected memory cells, depending on the magnetic field level of the noise. More specifically, data may be possibly erroneously written to the other unselected memory cells.
The typical example of such magnetic field noise is a magnetic field generated by currents carried to a power supply wiring and a ground wiring for supplying an operating voltage to peripheral circuits so as to perform data read and data write from and to the memory sections of the MRAM device. The currents carried to the power supply wiring and the ground wiring tend to peak during the operation of the peripheral circuits, so that the magnetic field noise from the wirings has a certain degree of intensity.
In the case where the power supply wiring and the like are arranged in the vicinity of the memory sections, i.e., in the vicinity of the tunneling magneto-resistance elements TMR or arranged on the memory sections for realizing high integration, in particular, it is necessary to take measures to prevent the lowering of an operation margin and erroneous data write caused by the magnetic field noise from the power supply wiring.